Heliospheric Crossings (and the Consequences)

byPaul GilsteronSeptember 30, 2009

Below you’ll see that I’m running Mike Brown’s sketch of the ‘new’ Solar System, one I originally ran with our discussion of Joel Poncy’s Haumea orbiter paper, which was presented at Aosta in July. The sketch is germane on a slightly different level today because as we look at how our views of the Solar System have changed over the years, we’ve learned how many factors come into play, including one Brown’s sketch doesn’t show. For surrounding the planets and nearer regions of the Kuiper Belt is the heliosphere, that bubble of solar wind materials whose magnetic effects help protect the inner system.

Image: Our view of the Solar System has gone from relatively straightforward to one of exceeding complexity. Credit: Mike Brown/Caltech.

Look at the heliosphere diagram below and you’ll see that while the eight planets are comfortably within it, our Pioneers and Voyagers are pushing toward or through the termination shock on their way to the heliopause. Galactic cosmic rays are shown pushing from deep space in toward the bow shock. Our new view of the Solar System must include the fact that the heliosphere does not extend to all of it. The Oort Cloud, that vast sphere of comets, is well outside it, and so would be those Kuiper Belt objects that wander too far from the Sun.

Image: Components of the heliosphere. Credit: NASA Ames.

How about a future mission to Sedna? Better be careful, because this odd object moves out to about 990 AU at aphelion. Our intrepid astronauts, having solved the propulsion problem, would now face galactic cosmic rays without the helpful shielding effects of the heliosphere. Galactic cosmic rays are subatomic particles — protons and some heavy nuclei — that have been accelerated to high velocity by supernova explosions. They’re enough of a problem on the interplanetary level, but become even more of one beyond the system.

All this comes to mind because we’re seeing an increase in cosmic ray intensities, some 19 percent higher than what we’ve seen in the last fifty years, according to Caltech’s Richard Mewaldt, who adds “The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions.” This NASA news release points to three culprits: a flagging solar wind, a decline in the Sun’s interplanetary magnetic field, and a flattening of the heliospheric current sheet where the polarity of the Sun’s magnetic field changes from a plus to a minus.

We’re safe enough where we are, of course, because the Earth’s atmosphere has allowed life to weather far worse cosmic ray fluxes. But if Mewaldt is right, we may have experienced a low level of cosmic ray activity for most of the space era. “We may now be returning to levels typical of past centuries,” says the scientist, reminding us how much we have to learn about the factors that make space flight within and without the system a hazardous enterprise.

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CarlSeptember 30, 2009, 17:22

Rama-style multi-generation vessels would have thick hulls for the centrifugal stresses, which would also be effective against the galactic cosmic rays. There was a hardcover book several decades ago… nonfiction, and I can’t recall the title… which had an engineering scheme for such mobile worlds. An iron-rich asteroid would be bored to its center. Charges of ice would be placed into the bore-holes, and sealed near the surface. The asteroid, perhaps moved more sunward, would be given a more rapid rotation while it was heated by huge solar parabolic mirrors. This was ideally to raise the body to molten heat, and the ice would become steam which would inflate the asteroid, providing a hollow structure in a single piece. It would then be cooled and outfitted for dwelling and voyage.

I imagine many here will smile at this grand notion… it may or may not be plausible, but the very idea would yield the largest single engineered structure humanity has yet built.

With any luck we will get the next best thing in a decade or two — a viable Kuiper Belt target somewhere in the path of Pluto Express. We won’t know for certain until an intensive search of the flight path beyond Pluto has been completed (it won’t even start for a couple of years yet), but there is cautious optimism that something worth dropping in on for a flying visit will crop up.

Plasma-magnets and improved superconducting magnets deployed as external loops will make magnetic shielding a practical approach to this issue.

But the recent estimate of a 3% cancer risk being reached after 200 days of exposure to cosmic rays implies that some kind of improved cancer tolerance will be the best approach for those wanting to live in space. I wonder if our resident biologist, Athena, might have any thoughts on that prospect. Can we come to some kind of new equilibrium with cancer? More anti-oxidants or periodic injections of tailored viruses? What’s biologically plausible?

The possibility of about 50 Dwarf Planets in the Kuiper Belt makes for some interesting manned mission scenarios. We will need shielding from galactic cosmic rays. Perhaps lead or other similarly dense materials combined with an artifical mini-magnetosphere could be of help here.

Fifty dwarf planets is a lot of territory to explore and on which to set up sub-surface many storied or many leveled colonies. If such sub-surface colonies had a per level population density of Earth but which contained 10 to 00 levels, each colony could support about 10 billion persons for a total of as much as one half a trillion persons.

Take into account the possibility that the Oort Could may also contain planetary bodies and the number of persons that our solar system might support becomes huge.

Many other star systems are likely to be very similar to our solar system in a qualitative sense and so the potential for the Milky Way Galaxy and eventually galaxies that are remote to support future human colonies is profound.

Cancer and mutations arising from bombardment by cosmic rays will be among the major challenges of long-term space travel. This would affect not only the crew but also the frozen embryonic stocks that a ship might carry. Germline mutations could doom the long-term prospects of the expedition.

Tailored viruses have at least four problems I can think of off the top of my head: site of integration, level of expression, cell type preference and the blood brain barrier. Also, you would have to add a viral cocktail containing many genes, hoping to bracket everything that’s affected. Stem cell replacement might be better, since it would renew both DNA and cells. That method has its own set of problems which overlap that of the viruses. Increasing the activity of radical-scavenging enzymes (peroxidases, catalases, dismutases) might be yet another approach, but you would need to make the boost reversible if you don’t want a slew of side effects: among other outcomes, they might end up attacking healthy tissue. We will also need to develop and perfect less problematic anti-cancer therapies, chemotherapy agents in particular.

In short, we can construct biological tools to contain or repair cosmic ray damage, though it will take time to fine-tune them and make them less harmful than what they’re meant to combat. In the end, I think we will employ a combination of all the techniques I listed above (and then some) to tackle the problem.

“The way the US manned space program is headed, we won’t have to worry about astronaut exposure to radiation :( ”

I share some of your misgivings. I grew up during Projects Mercury/Gemini/Apollo, which were exciting to watch unfold on television. There were numerous media featuring von Braun himself back then. I was certain we were at the beginning of the new age of human exploration.

It was a Pioneer Spirit, to be sure. I say this Spirit is not dead; this news forum is evidence of it. If we survive to move into other systems, it is in part because of the forethought that goes on here.

What must be accomplished shall have to be multinational, and such ventures are undertaken now. These are the Dawn Ages.

All I want to know is how thick a coating of lead is needed to stop the CBR from messing things up in our bodies? I don’t care about cost. I don’t care how many launches it takes to get the shielding up there. I don’t care about any of that $ talk. The shielding can be sent up as plates that get bolted on the ship/habitat AFTER the thing has been put up there! Does it need to be a meter thick (two meters)? What about cement or geopolymer concrete or water laced with ‘xyz’ ? Heck, back in WWII there were plans to build an aircraft carrier out of ice laced with wood pulp, and that concoction was fairley bullet resistant.

I remember reading that the O’neil type colony structurers were supposed to be covered with six feet thick of lunar regolith for protection from CBR and minor meteoric impacts. So…why not!?

I wanna know…I gotta know what kind and how much junk has got to be slathered about the hull of my ship so I can live in the Oort cloud and stop payin’ taxes!

I agree with James M Essig that this is a very interesting thread so lets add another factor to discussion. Given that the Alpha Centuari system probably has a similar Heliosphere and Heliopause, and we are directly adjacent to each other is it not possible that we would never actually enter “real inter-galactic space” when traveling between the two star systems. In fact, for purposes of Space Exploration it may even be possible to redraw “the New Solar System” pictorial above to include the entire Alpha Centauri System as part of a single “Sol/Alpha Solar System” spanning almost 5 Light Years. There is strong emerging evidence that traveling from our Solar System to Alpha Centauri is going to be a much different and easier trip (assuming no Warp Drive) then having to travel through real inter-galactic space to get to a star system 5-50 Light Years away. In addition, if we ever develop viable room temperature super-conductivity it may be possible according to Michio Kaku to develop a form of a pseudo-antigravity/field propulsion system in which a space ship would exploit the gravity of various objects between the Sol system and the Alpha Centuri systems to execute a form of “Lily pad” travel between the two Star systems. The basic contention here is that we may need to start thinking about Sol and Alpha Centuari as being part of a single integrated system for travel purposes, at least for the next 100,000 years or so.

OT, but I haven’t seen anything about the New Horizons mission doing any study of the heliopause subsequent to its Kuiper Belt work. Is the heliopause maybe too far away in the direction New Horizons is traveling?

I really like the idea of the solenoidal shaped torus spaceship design, it could provide multiple levels and multiple gravities, perhaps it would be like living in an extreamily twisted mall with enough variety and eye-candy to keep the human mind interested on long journeys. Oh, and of course the solenoidal design makes for a wonderful place to park your excursion vehicles and raw material bins to feed your refineries.

My thoughts on the shielding resemble past comments from the ‘gallery’. But I was thinking along the lines of “big dumb machine’, where overlaping plates like a chess board are then again overlaped at their junctions by containers filled with lead which are supported by the hardened steel plates that are attached to the containers via shock absorbing springs (think: U.S. Gov. under ground environments where vital equipment sits on train carrage springs) that support more overlapping plates of a similar or alternate shield substance like…pykrete: Here I’m thinking of anti missle armament platting that one may find on tanks that, when struck, explode outward away from the primary armor. Where here, by using the pykrete, an impactor would be hitting the soft stuff first after breaching the container and thusly protect the primary radiation shielding located underneath. Imagine a multi-layer corn on the cob cellular arangement that is sacrifial and can be repaired with easily attainable materials (a container that can be filled with anything) superconducting coils could be sandwiched between the layers and could piggyback the cold temperatures of space since they would be in shadow (same for inside the torus). The added plus of harvesting energy scavaging methods between two temperature extreems is also possible here. Forward of the ship and supported by Orion type shock aborbers would be the leading deflector plate (or ring) with similar hero sandwich-like shielding. The front can take the hit, if that happens, and is no longer needed at final destination (or keeping it for surplus materials makes better sense). And of course, the whole monstrosity, has additionally, the magnetic shielding to slipstream the lesser particles away. Or maybe this idea is too big to shove to Alpha centauri (or mabe not), or pehaps it would be better suited to hang out in an asteroid belt? If the high tecnology should fail, the bruit force of mass will save all.

Adding to my sci fi, why not have the crew supplied with anti-radiation uniforms? The clothing doesn’t have to be perfect, just as long as the major vital organs get covered: No I’m not talking about the lead bibs in the dentists office or gothic latex cat suits (or maybe I am), but if any of you have seen any of the dry-suits that we have these days, then style is gonna be the least of our worries. Think coveralls with an inner lining vest of that rubbery Dupont stuff…should be quite comfortable. Redundancy is my thought, and keep the safe rooms for added peace of mind.

I’ve been looking up bomb and fallout shelters, so using lead, cement, water, polyethelene or other things with lots of hydrogen in their makeup as radiation shielding should stave off the wolves. These are simple things and the list is by no means complete or evolved. i.e. there is stuff we’ve got now that will work, and be damned the mass I say! The idea of using tinfoil however, just makes my skin crawl. I want a ship/habitat that will lass 500 years and twice as long after that.

The “new solar system” diagram appears to show two or three separate red lines coming inside Neptune’s orbit. I thought Pluto was the only dwarf planet that did that? Is this a conjecture, or is one of the others’ orbits already known to cross?

Elon, I should also mention Ceres as a dwarf planet, but it’s not in the category you’re talking about — i.e., crossing Neptune’s orbit. I’ll get some help from some of our resident astronomers on this, I hope, but if I recall correctly, there are a number of KBOs (though not dwarf planets) that do cross Neptune’s orbit. Orcus, Rhadamanthus, and Ixion come to mind as KBOs with close interactions with Neptune, though I don’t recall which of these actually crosses its orbit.

The vast majority of the red orbits are for objects which will probably eventually be assigned dwarf planet status but the IAU hasn’t got round to doing this yet.

As for the new solar system being a view of “exceeding complexity”, I disagree. The new model recognises that beyond Neptune is another “asteroid belt”, rather than a swarm of small (but still major) planets. This seems to me a far more intuitive way of describing the solar system. The precise wording of the IAU definition is unfortunate, but the new structure makes sense.

The current view of the entirety of the Solar System is exceedingly complex when compared with the classical view of the system. As surprising as it may be, there are still people alive who were born in the time when the known Solar System comprised of the Sun, eight planets and their attendant moons, and a handful of asteroids neatly slotted between Mars and Jupiter, with just the odd comet or two to spice things up every now and then.

No NEO asteroids, no Trojans, no KBOs, no icy dwarf planets, no Oort cloud. That we can and do categorize these objects as we discover these new populations doesn’t really change the fact that the Solar System is a much more complex and random place than people envisaged for hundreds of years.

Re the comment about radiation damaging embryos during long voyages: By the time we are making those long voyages, we will be able to synthesize a cell’s worth of DNA and insert it into a cell to make a viable organism. There will be no need to store genetic information in actual non-redundant physical DNA.

Chris, what alleles are you going to insert in that DNA that will maintain both integrity and diversity? And that doesn’t take into account such items as correct maternal gradients and imprinting. To put it another way, if this were as easy as that, it would be doable by now — we can synthesize DNA at will by PCR and make genes, even artificial chromosomes, at will by recombinant DNA techniques.

Water is among the best radiation shields. I think I said it in a previous post here: have an ocean next to the starship hull! It will take care of all kinds of items on the list — from food to radiation.

Better yet, make it an Orion (ca. 1958) ship, as Pournelle used in FOOTFALL; launch from a polar tower with the first pulse from conventional high explosive, above a steel reflector, to avoid fallout; clean bombs thereafter exploding in midair, without the U238 jacket which causes fallout in military nukes.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last eleven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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